Dr. Conrad HeatwoleCenter for Watershed Studies
Virginia Tech, Blacksburg
Study watersheds – Magodi
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#0Luelo
MphiriKamwamphula
Kanyanga
Stream gage Weather station Rain gage Manual raingage
Paired Forest/Ag. Watersheds
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Gate4
Khuyu school
Chazovu school
Kamwamphul
a
Luelo
ZAWA
gate
Forested watershed
Agricultural watershed
Cropland expansion 1989-2007
1989Landsat
Cropland expansion 1989-2007
2002Landsat
Cropland expansion 1989-2007
2007Ikonos
Cropland expansion 1989-2007
Cropland expansion 1989-2007 1989Landsat
Cropland expansion 1989-2007
1989Landsat
Polygons are cleared areason May 2007 EnsoMosaic
Slope map of area
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Gate4
Manga
Emusa EDP
Kanga Depot
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> 45
Dambo watershe
dsPaired
watersheds
Slope (%)
Slope calculated from 30m elevation grid derived from SRTM data using cubic interpolation.
Relation of cleared areas to landscape position
Maps of elevation and slope with the Enso cleared areas overlayed
Relationship between slope and cleared areas Cleared areas (digitized from 2007
Enso/Mosaic aerial imagery as seen in above slides) are overlaid on the slope map. Slope data is classified in 1% increments.
Areas at different slope values are tabulated. Cumulative areas determined and graphed as a % of the area.
Comparing slopes of cleared land in hill and plateau regions
Graph of cumulative percent area less than a certain slope
Data is only for cleared area on the 2007 Enso/Mosaic
Example – at 4% slope:45% of hill area and 83% of
plateau area is less than 4% Conversely, 55% of hill area
is greater than 4% slope, but only 17% of the plateau area.
Cumulative distribution of cleared area based on slope
Comparing slopes of cleared land for three watersheds
Observations: Kamwamphula is steeper than
Luelo; both are much steeper than the plateau area
While about 13% of the plateau watershed is greater than 4% slope, 45 to 60% of the hill area is
Cleared areas tend to the lower slopes, but surprisingly represent the range of slopes in the watershed.
cleared areas are not exclusively on the low slopes
The curves for the more fully cleared Luelo are closest, indicating that over time, cleared land represents the whole watershed – not just flatter areas
The curves for Kamwamphula are further apart, showing that initial clearing is on flatter areas. However, the trend seen in the Luelo is to be expected.
Cumulative distribution of area based on slope for a plateau
watershed and two watersheds in the hill region